The present invention generally relates to a tubular prosthesis and methods for delivery into a body channel. More particularly, the present invention relates to an improved delivery system for delivering a stentless bioprosthesis comprising a collapsible elastic valve or a biological graft at a desired anatomical site of the body channel for implantation.
A prosthetic heart valve may be used to replace a diseased natural heart valve in a human patient. Similarly, a prosthetic venous valve may be used to replace a dysfunctional natural venous valve in a patient. Mechanical heart valves typically have a rigid orifice ring and rigid hinged leaflets coated with a blood compatible substance such as pyrolytic carbon. Other configurations, such as ball-and-cage assemblies, have also been used for such mechanical valves. A mechanical heart valve cannot be retracted radially and delivered by a catheter-based delivery system.
In contrast to mechanical heart valves, bioprosthetic heart valves comprise valve leaflets formed of biological material. Many bioprosthetic valves include a support structure, or stent, for supporting the leaflets and maintaining the anatomical structure of the valve. Stented bioprosthetic valves generally are prepared by chemically cross-linking a retrieved pig""s heart valve, followed by attaching it to a stent. The stent provides structural support to the valve and, with a sewing cuff, facilitates attachment of the valve to the patient by suturing. Gabbay in U.S. Pat. No. 5,935,163 discloses a natural tissue heart valve prosthesis with a substantially flexible annular ring to provide additional support, the entire contents of which are incorporated herein by reference.
One of the major functions of stents is to serve as a framework for attachment of the valve and for suturing the valve into place in the human patient. Various stent designs have been implemented in a continuing effort to render valve implantation simpler and more efficient. Inevitably, however, a stent limits interactions with aortic wall dynamics and tends to inhibit natural valve movement. This results in post-operative transvalvular gradients with resultant additional work burden on the heart. In addition, a stent causes a reduction in size of the bioprosthetic valve that can be placed in a particular location, since the stent and sewing cuff occupy space that otherwise would be available for blood flow. Recently biodegradable stents are disclosed, for example, U.S. Pat. No. 5,895,420 to Mirsch II, et al. and U.S. Pat. No. 5,489,297 to Duran, to limit disadvantage of the valve stenting to a shorter time of implantation until it is biodegraded. Both patents are incorporated herein by reference.
Some bioprosthetic valve manufacturers have attempted to develop methods and systems to ease the implantation of stented valves, including special catheter-based delivery system. Both of U.S. Pat. Nos. 5,840,081 and 6,168,614 to Andersen et al. disclose a minimally invasive percutaneous delivery system with a balloon catheter. A stented valve prosthesis is contractively mounted within a lumen of the catheter during delivery. At a desired anatomical site, the prosthesis is pushed out of the catheter tip and self expands. Lutter et al. reported an experimental study on percutaneous transluminal replacement of the aortic valve (81st American Association for Thoracic Surgery Program Book pp. 174, May 6-9, 2001, San Diego, Calif.). They concluded that aortic valve stents with a self-expandable metallic stent can be successfully implanted by transluminal catheter technique without the need of opening the chest.
Porter in U.S. Pat. No. 5,064,435 discloses a catheter-based apparatus and methods for releasing a self-expandable prosthesis by a conventional pushing mechanism. The above-mentioned approaches are satisfactory for delivering a stented prosthesis having an external rigid support adapted for receiving the pushing force. A self-expanding prosthesis often is preferred over a plastically deformed device. Resilient prosthesis can be deployed without dilatation balloons or other stent expanding means. A self-expanding prosthesis can be preselected in accordance with the diameter of the body channel or other anatomic site for fixation. While deployment requires skill in positioning the prosthesis, the added skill of properly dilating the balloon to plastically expand a prosthesis to a selected diameter is not required. Also, the self-expanding prosthesis remains at least slightly compressed after fixation, and thus has a restoring force which facilitates acute fixation.
Stentless valves have demonstrated better hemodynamic function than stented valves. This is because a stentless valve is sewn directly into the host tissues, without the need for extraneous structure such as a sewing cuff. Such extraneous structures inevitably compromise hemodynamics. A stentless valve closely resembles a native valve in its appearance and function, and rely upon the patient""s tissues to supply the structural support normally provided by a stent. Quintero et al. in U.S. Pat. No. 5,197,979, NguyenThien-Nhon in PCT W.O. No. 99/33412, and Vrandecic Peredo in PCT W.O. No. 00/00107 all disclose stentless valve structure and function, the entire contents of which are incorporated herein by reference.
The main disadvantage to stentless valves has been in their difficulty of deployment and implantation, particularly in a catheter-based percutaneous route. With recent scientific advancements in robotics, instrumentation and computer technology, a minimally invasive catheter-based delivery system for a stentless bioprosthesis is imminent. There is currently a clinical need for deploying a tubular stentless prosthesis, such as a stentless valve or a vascular graft without a rigid support, into a body channel, preferably by a percutaneous approach. The catheter-based percutaneous delivery system as compared to an open-cavity surgery will greatly reduce the patient""s hospital stay and improve recovery.
It is an object of the present invention to provide a method for delivering a stentless bioprosthesis in a body channel, the method comprising percutaneously introducing a catheter into the body channel, wherein the catheter contains the radially elastic stentless bioprosthesis at a retracted state; and disengaging said stentless bioprosthesis out of a distal opening of the catheter by a pulling mechanism. In one embodiment, the pulling mechanism further comprises an engaging element coupling to a distal portion of the stentless bioprosthesis. In another embodiment, the method further comprises separating the stentless bioprosthesis from said engaging element.
The stentless bioprosthesis of the present invention has the common characteristics of soft, collapsible radially, collapsible longitudinally, and without any rigid support onto or around the bioprosthesis.
It is another object of the present invention to provide a catheter for delivering a tubular prosthesis to an anatomical site in a body channel, the catheter comprising an elongated delivery member located inside the lumen of the catheter, the elongated delivery member having an engaging element at the distal end of the elongated delivery member, wherein the engaging element is adapted for engaging and disengaging a distal portion of the tubular prosthesis. In one embodiment, the catheter further comprises a delivery mechanism at the handle that is coupled to the elongated delivery member. The delivery mechanism is adapted for pulling the distal portion of the tubular prosthesis out of the catheter shaft during a deployment or releasing stage. In another embodiment, the engaging element comprises a plurality of releasable sutures, gripping jaws or bioadhesives.
It is still another object of the present invention to provide a method for delivering a tubular stentless prosthesis to an anatomical site in a body channel, the method comprising the steps of introducing a catheter into the body channel, wherein the catheter contains the tubular stentless prosthesis at a retracted state; advancing the catheter to the anatomical site; maintaining a distal portion of the tubular stentless prosthesis in place relative to the anatomical site; disengaging the catheter from the tubular stentless prosthesis adapted for self-expanding said prosthesis from the retracted state; and withdrawing said catheter from the body channel
The tubular stentless prosthesis of the present invention generally includes, but not limited to, a vascular graft, a synthetic vascular graft, a biological vascular graft, a cardiac valve, a valved conduit, a venous valve, and other stentless implantable devices. The xe2x80x9ctubular stentless prosthesisxe2x80x9d is essentially synonymous with the xe2x80x9clongitudinally collapsible prosthesisxe2x80x9d in the invention.
In a further embodiment, the method comprises another step of coupling the prosthesis into tissue of the body channel, wherein the coupling means may include stapling, adhering, stenting, anchoring and the like.